FIG. 1 illustrates a heterogeneous network wireless communication system 100 including a macro base station eNB1 and a micro base station eNB2. In the description of the present invention, the term “heterogeneous network” refers to a network wherein a macro base station 110 and a micro base station 120 co-exist even when the same RAT (Radio Access Technology) is being used.
A macro base station 110 refers to a general base station of a wireless communication system having a broad coverage range (service provision area) and a high transmission power. The macro base station 110 may also be referred to as a macro cell. The micro base station 120 may also be referred to as a micro cell, a pico cell, a femto cell, a home eNB (HeNB), a relay, and so on. More specifically, the micro base station 120 corresponds to a smaller version of the macro base station 110. Accordingly, the micro base station 120 may independently perform most of the functions of the macro base station. Herein, the micro base station 120 may correspond to an overlay base station, which may be installed in an area covered by the macro base station, or to a non-overlay base station, which may be installed in a shadow area that cannot be covered by the macro base station. As compared to the macro base station 110, the micro base station 120 has a narrower coverage range and a lower transmission power and may accommodate a smaller number of terminals.
A terminal 130 may directly receive services from (or be served by) the macro base station 110 (hereinafter referred to as a macro-terminal) or may directly receive services from (or be served by) the micro base station 120 (hereinafter referred to as a micro-terminal). In some cases, a terminal 130 present within the coverage area of the micro base station 120 may receive services from the macro base station 110. FIG. 1 shows a state in which the terminal 130 is connected to the micro base station 120.
Depending upon whether or not the terminal has limited access, the micro base station may be categorized into two different types, the first type being a CSG (Closed Subscriber Group) micro base station, and the second type being an OA (Open Access) or OSC (Open Subscriber Group) micro base station. More specifically, the CSG micro base station may serve only specific terminals that are authorized, and the OSG micro base station may serve all types of terminals without any particular access limitations.